1. Field of the Invention
The present invention generally relates to a dual-use jack, which is an audio signal output jack, designed to receive a headphone plug or a line output plug, and more particularly to a method and circuitry for determining whether a headphone plug or a line output plug is connected to the dual-use jack.
2. Description of the Related Art
Portable electronic devices such as portable audio players, digital cameras and digital video cameras have a jack for headphone. With function and performance developments of the portable electronic devices as well as wide spread use thereof, the portable electronic devices are also equipped with another jack (i.e., stereo terminal) that is used for line output.
Separately providing one jack for headphone and another jack for line output will hinder size reduction and weight reduction of the portable electronic device. Thus, a single jack (or dual-use jack) is often used, which can be used for the headphone plug and line output plug. When a single dual-jack is used, it is difficult for the electronic device to know for which purpose the jack is used (i.e., for headphone or for line output). In order to know usage of the jack that has received a plug, a certain voltage is applied across a load resistance of the plug (i.e., headphone plug or line output plug), and a resulting current is measured. The current value is used to obtain (calculate) a value of the load resistance, and the calculated value of the load resistance will determine the usage (i.e., whether the jack is connected to the headphone plug or to the line output plug) of the dual-use jack. Japanese Patent Application Kokai (Laid-Open) No. 2002-141980 discloses a control unit that can determine the usage of such dual-use jack after a test current is caused to flow through the plug.